"Backup plan" does not sound like a business strategy term to me. It can be used broadly.
You could also consider the following:
- an ace up your sleeve; to have an ace up your sleeve
- have (something) up (one's) sleeve
To have a secret plan, idea, or advantage that can be utilized if and when it is required. A reference to cheating at a card game by hiding a favorable card up one's sleeve. I have a few tricks up my sleeve if he decides to pursue legal action against me. She has a card up her sleeve if they ever try to fire her, since she knows about the boss's unscrupulous business practices.
- trump card
- A resource used to gain an advantage over others, often by being held and then used at an opportune time. I have a feeling the prosecution still hasn't played their trump card in this trial—I expect a big revelation during tomorrow's testimony.
- plan B
A secondary "backup" plan to be undertaken should one's original plan fail or prove unfeasible. We're running a bit late, so how about plan B: Instead of getting dinner before the movie, let's just get some popcorn at the theater and eat something proper afterward. Well, the diagnostics test didn't reveal any issues with the server. Do you have a plan B?
The first two often suggest that you strongly believe, or are certain, that the alternative will succeed.
A last resort (as you mentioned in a comment) is often an option you use after multiple alternatives failed and is used out of desperation. It's often your last hope and not necessarily an option you believe will succeed.